Those temperature fluctuations arise from quantum-fluctuations in the early universe and, along with inflation, they explain why the universe contains the structure that it does. Measuring temperature fluctuations in the cosmic microwave background requires extremely precise temperature measurements at many points in the sky.

Enough photons must be observed to reconstruct the black-body spectrum from which the temperature is determined. But in the little bangs created in the laboratory, only a few thousand particles can be created so a similar map cannot be made for each event. But whereas there is only one universe, billions of collisions are created in the lab. The figure below shows a schematic of the expansion of the universe and a schematic of the expansion of a collision between Gold nuclei.

By studying data from millions of these collisions, we attempt to find evidence for hot-spots in the Quark-Gluon-Plasma. The analysis of the cosmic microwave background radiation has several similarities to the analysis of correlations between particles produced in Gold collisions.